Implement sequence-related functions for ODBC backend.

Determine which kind of database we're connected to and implement either
get_next_sequence_value() or get_last_insert_id() using database-specific
queries depending on it.

Signed-off-by: Vadim Zeitlin <vz-soci@zeitlins.org>

src/backends/odbc/session.cpp

@@ -7,6 +7,7 @@
 
 #define SOCI_ODBC_SOURCE
 #include "soci-odbc.h"
+#include "session.h"
 
 using namespace soci;
 using namespace soci::details;
@@ -95,6 +96,88 @@ void odbc_session_backend::rollback()
     reset_transaction();
 }
 
+bool odbc_session_backend::get_next_sequence_value(
+    session & s, std::string const & sequence, long & value)
+{
+    std::string query;
+
+    switch ( get_database_product() )
+    {
+        case prod_firebird:
+            query = "select next value for " + sequence + " from rdb$database";
+            break;
+
+        case prod_oracle:
+            query = "select " + sequence + ".nextval from dual";
+            break;
+
+        case prod_postgresql:
+            query = "select nextval('" + sequence + "')";
+            break;
+
+        case prod_mssql:
+        case prod_mysql:
+        case prod_sqlite:
+            // These RDBMS implement get_last_insert_id() instead.
+            return false;
+
+        case prod_unknown:
+            // For this one we can't do anything at all.
+            return false;
+
+        case prod_uninitialized:
+            // This is not supposed to happen at all but still cover this case
+            // here to avoid gcc warnings about unhandled enum values in a
+            // switch.
+            return false;
+    }
+
+    s << query, into(value);
+
+    return true;
+}
+
+bool odbc_session_backend::get_last_insert_id(
+    session & s, std::string const & table, long & value)
+{
+    std::string query;
+
+    switch ( get_database_product() )
+    {
+        case prod_mssql:
+            query = "select ident_current('" + table + "')";
+            break;
+
+        case prod_mysql:
+            query = "select last_insert_id()";
+            break;
+
+        case prod_sqlite:
+            query = "select last_insert_rowid()";
+            break;
+
+        case prod_firebird:
+        case prod_oracle:
+        case prod_postgresql:
+            // For these RDBMS get_next_sequence_value() should have been used.
+            return false;
+
+
+        case prod_unknown:
+            // For this one we can't do anything at all.
+            return false;
+
+        case prod_uninitialized:
+            // As above, this is not supposed to happen but put it here to
+            // mollify gcc.
+            return false;
+    }
+
+    s << query, into(value);
+
+    return true;
+}
+
 void odbc_session_backend::reset_transaction()
 {
     SQLRETURN rc = SQLSetConnectAttr( hdbc_, SQL_ATTR_AUTOCOMMIT,

src/backends/odbc/soci-odbc.h

@@ -243,6 +243,11 @@ struct odbc_session_backend : details::session_backend
     virtual void commit();
     virtual void rollback();
 
+    virtual bool get_next_sequence_value(session & s,
+        std::string const & sequence, long & value);
+    virtual bool get_last_insert_id(session & s,
+        std::string const & table, long & value);
+
     virtual std::string get_backend_name() const { return "odbc"; }
 
     void reset_transaction();